This invention relates to a power safety device for use in a cable television ("CATV") system in which the converter for converting portions of the television signal on the cable network to the television signal which is appied to the subscriber's television receiver, or other electronic circuitry for delivering television signals to the subscriber, is located outside the subscriber's premises, and in which electrical power for the off-premises converter or other electronic circuitry is provided by the subscriber via the subscriber's drop cable.
In a conventional CATV system, when a subscriber contracts with the CATV service company to subscribe to receive desired television channels, the company installs a CATV converter indoors in the subscriber's house. The CATV converter is powered by being plugged into an ordinary AC outlet in the subscriber's home. The entirety of the television signal is delivered via a drop cable into the subscriber's home, and the converter allows selection and viewing of only those portions of the television signal for which the subscriber has contracted.
Delivering the entirety of the television signal to the subscriber creates at least two security problems. First, the subscriber may be able to modify the CATV converter to view CATV programs on nonsubscribed channels, resulting in a loss of revenue to the CATV system operator. Second, the subscriber may move and take the expensive leased CATV converter with him, although the CATV service company is entited to repossess the converter. Again, the CATV service company suffers a loss.
To prevent the misappropriation of CATV services and of CATV converters, the CATV converter or other electronic circuitry (such as circuitry to jam or interdict one or more portions of the television signal) may be placed outside of the subscriber's home, for example in a tap-off device mounted on a telephone pole. However, once the converter unit or other circuitry is installed outside of the subscriber's home, another means must be provided for powering the circuitry.
One way to power the external circuitry is to transmit power signals from the head end or some other point "upstream" of the external circuitry via the cable network. This approach has been used, for example, in conventional systems to power signal distribution ampifiers and tap-off devices placed at various points of the cable network. However, providing power in this manner requires the CATV service company to provide a large amount of electrical power over long distances, and increases the expense and complexity of the cable network.
Another way to power the circuitry of externaly located tap-off devices is to supply power from the subscribers served by the tap-off device. Such power may conveniently be supplied via the drop cables connecting individual subscriber premises to the tap-off device. A power supply device for providing power in this manner is described in commonly assigned U.S. patent application Ser. No. 616,384, entitled "Power Supply System For CATV Tap-Off Unit" and filed May 31, 1984.
Delivering power to external tap-off devices via individual subscriber drop cables, however, can potentially create a safety problem in the event the drop cable connecting the tap-off device to the power supply in the subscriber's house is cut, broken or disconnected. In such an event, the power supply in the subscriber's house would continue to apply electrical power to the cut, broken or disconnected drop cable, thus presenting an electrical shock hazard to individuals advertently or inadvertently coming into contact with the drop cable.
In view of the foregoing, it is therefore an object of this invention to minimize electrical shock hazards assooiated with CATV systems in which at least a portion of the electrical power required to power such systems is supplied by individual subscribers via the drop cables connecting the subscribers to the cable network.